Several thousand human sera from Africa, the Mediterranean region, Central and Southeast Asia were screened by plaque reduction neutralization method against 8 Phlebotomus fever virus serotypes occurring in the Old World. Results of these studies indicate that Naples and Sicilian virus infection is common among residents of North Africa, the Mediterranean and Central Asia. Karimabad virus neutralizing antibodies were found only in Iran and the Soviet Union. Antibodies against the other 5 Phlebotomus fever serotypes were uncommon, suggesting that the latter agents infrequently infect man and are of little public health importance. A new Vesiculovirus, designated Isfahan virus, was isolated, studied and characterized. Serologic evidence of human infection with this agent was demonstrated. BIBLIOGRAPHIC REFERENCES: Tesh, R. B. and Papaevangelou, G.: Effect of insecticide spraying for malaria control on the incidence of sandfly fever in Athens, Greece. Am. J. Trop. Med. Hyg. 26:163-166, 1977. Tesh, R., Saidi, S., Javadian, E. and Nadim, A.: Studies on the epidemiology of sandfly fever in Iran. 1. Virus isolates obtained from Phlebotomus. Am. J. Trop. Med. Hyg. 26:282-287, 1977.